linux-kernel - Re: [PATCH v3 02/15] mm: introduce is_huge

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Message-ID: <20211110125936.GR1740502@nvidia.com>
Date:   Wed, 10 Nov 2021 08:59:36 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     akpm@...ux-foundation.org, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com, mika.penttila@...tfour.com,
        david@...hat.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        songmuchun@...edance.com, zhouchengming@...edance.com
Subject: Re: [PATCH v3 02/15] mm: introduce is_huge_pmd() helper

On Wed, Nov 10, 2021 at 08:58:35PM +0800, Qi Zheng wrote:
> 
> On 11/10/21 8:29 PM, Jason Gunthorpe wrote:
> > On Wed, Nov 10, 2021 at 04:40:44PM +0800, Qi Zheng wrote:
> > > Currently we have some times the following judgments repeated in the
> > > code:
> > > 
> > > 	is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)
> > > 
> > > which is to determine whether the *pmd is a huge pmd, so introduce
> > > is_huge_pmd() helper to deduplicate them.
> > 
> > Isn't this pmd_leaf() ?
> 
> Currently, the implementation of pmd_leaf() does not include
> pmd_devmap() checks. 

Are you sure? I thought x86 did via the tricky bit checks?

> But considering the semantics of pmd_leaf(), the "devmap" pmd should
> also belong to "leaf" pmd. Maybe we should modify pmd_leaf() to make
> it more semantically consistent?

I would prefer that..

Jason